Cambodia and China will hold joint annual military drills from Thursday, an official said, amid US concerns that Beijing could use a Cambodian naval base to expand its influence in the region.

A Chinese warship docked in the coastal city of Sihanoukville on Monday morning, bringing troops and materials for the exercises, Cambodian army spokesman Thong Solimo told reporters in Phnom Penh.

More than 2,000 troops, including 760 Chinese military personnel, will participate in the drills at a training centre in central Kampong Chhnang province and at sea off Preah Sihanouk province, Solimo said.

Cambodia has long been a staunch ally of China, receiving billions of dollars in investments.

In December, two Chinese warships made a first visit to Cambodia's Ream naval base near the port city of Sihanoukville.

Washington says Ream, which is being upgraded by China, could give Beijing a key strategic position along the coast of the Gulf of Thailand, near the disputed South China Sea, which China largely claims.

But Cambodian officials have repeatedly denied the base is for use by any foreign power.

After Cambodia dismantled facilities at Ream, built partly with American funding and having played host to US military exercises, China began funding its renovation.

Last year, Cambodian officials denied a new 363-metre (1,190-foot) pier at Ream was intended to berth aircraft carriers.

The 15-day joint Cambodian-Chinese drills, dubbed Golden Dragon, will involve 14 warships -- three from China -- two helicopters and 69 tanks, and include live-fire, anti-terrorism and humanitarian exercises, Solimo said on Monday.

"This year's drills are bigger than previous ones both in terms of military personnel and materials," he said, adding that China would cover the cost of the exercises.

The first Golden Dragon drills were held in 2016.

Defence ministry spokesman Chhum Socheat said in a Facebook post last week that the Chinese warships that anchored at Ream in December were "to help train Cambodian naval personnel and to prepare for the Golden Dragon exercises".

He said the Chinese vessels would test the "Ream Naval Base that China is constructing for Cambodia", and denied Chinese troops would be stationed at the base.